This invention relates to a chuck closing mechanism, and more particularly to an improved, hydraulically operated chuck closing mechanism that is particularly adapted for use with automatic screw machines.
U.S. Pat. No. 4,799,696, which is assigned to the same company as the present application, discloses a chuck closing mechanism which is particularly suitable for use with an automatic screw machine. That particular mechanism utilizes a mechanically operated camming device for selectively opening and closing a tubular collet through the bore of which bar stock is intermittently advanced into registry with associated cutting tools on the machine. The collet is attached to the forward end of an inner tubular spindle, which is fixed coaxially within, but which rotates with an outer spindle. The outer spindle is reciprocable relative to the inner spindle, and selectively into and out of a collet closing position in which its forward end advances over the collet to force the collet teeth radially inwardly to a closed position around a piece of bar stock.
Chuck closing mechanisms of the type disclosed in the above-noted U.S. Pat. No. 4,799,696 are very effective, but are rather noisy in operation and are subject to wear after repeated use. Applicants have discovered that objectionable noise and wear can be minimized, if not eliminated, by utilizing a hydraulically operated device for opening and closing the associated collet, rather than a cam-operated device.
Heretofore efforts have been made to operate chuck closing mechanisms hydraulically. U.S. Pat. No. 3,168,322, for example, discloses a spring-loaded draw bar which functions normally to retain an associated collet chuck in a closed or tool-gripping position. To release the collet rotation of the draw bar must be stopped, after which hydraulic fluid under pressure is supplied to a chamber to cause the draw bar to be retracted against the resistance of the collet-closing spring mechanism. A major problem with this mechanism, however, is that it is not suitable for feeding bar stock. Instead, it is directed to a removable collet designed especially for holding a tool or tool holder having thereon specially shaped keyways and annular rib means, which cooperate with corresponding keys and rib means formed on the collet holder, and the inner peripheral surface of the collet itself. It is therefore impossible to feed bar stock through the draw bar that manipulates the collet closing head.
In contrast to the apparatus disclosed in U.S. Pat. No 3,168,322 the automatic screw machine to which the chuck closing mechanism of this invention as related, utilizes a collet which is designed to feed bar stock through its bore, and which is operable even while being rotated about its axis.
Accordingly, it is an object of this invention to provide for a multiple spindle screw machine an improved, hydraulically operated chuck closing mechanism which is very quiet during operation, and which tends to show very little wear during prolonged use.
Still another object of this invention is to provide for a machine of the type described, an improved chuck closing mechanism which is relatively simple to operate and inexpensive to produce, as compared to prior such devices.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawing.